Measurement of the energy response of the ATLAS calorimeter to charged pions from W^±→τ^±(→π^±ν_τ)ν_τ events in Run 2 data

The energy response of the ATLAS calorimeter is measured for single charged pions with transverse momentum in the range 10 < pT < 300 GeV. The measurement is performed using 139 fb⁻¹ of LHC proton–proton collision data at √s = 13 TeV taken in Run 2 by the ATLAS detector. Charged pions originating from τ -lepton decays are used to provide a sample of high-pT isolated particles, where the composition is known, to test an energy regime that has not previously been probed by in situ single-particle measurements. The calorimeter response to single-pions is observed to be overestimated by ∼2% across a large part of the pT spectrum in the central region and underestimated by ∼4% in the endcaps in the ATLAS simulation. The uncertainties in the measurements are 1% for 15 < pT